The present invention relates to ceramic capacitors used in various kinds of apparatus, such as a ballast circuit of an LCD backlight inverter, a primary/secondary snubber circuit in a switching power supply, a horizontal resonance circuit of a TV receiver/CRT display, an inverter fluorescent lamp, a high voltage/pulse circuit of an electronic appliance, a surge protection circuit in a communication modem; more specifically, the ceramic capacitors that provide a suppressed self heat-generation property and a low loss even in the high frequency/high voltage operating conditions.
Large screen-size/high picture-quality CRT displays and LCD displays have acquired an increasing popularity. At the same time, down-sizing of the switching power supply circuit is a recent trend in the industry. The ceramic capacitors, among the key passive components used in these devices, are required to be able to operate under the operating conditions of higher frequency and higher voltage.
In addition to the more stringent operating conditions, the ceramic capacitors are particularly requested to be more compact and lighter in weight to meet the downsizing trends in the switching power supply circuits and the DC-DC converter circuits.
The ceramic capacitors are facing another task. A ceramic capacitor has been structured of a disc-shape dielectric ceramic element assembly and an electrode provided on both surfaces in the main area of the disc-shape dielectric ceramic element assembly, each of the electrodes being connected with a lead wire, and the whole structure being covered by an appropriate molding material. As to the electrode material for ceramic capacitors, silver (Ag) has long been used. The Ag electrode, however, exhibits a substantial self heat-generation and an electro-migration as well.
In place of the Ag electrodes, electrodes made of a cheaper base metal, such as copper (Cu), nickel (Ni), are used among the recent ceramic capacitors. The electrodes made of Cu or other base metals are provided by baking in a neutral or reductive atmosphere in consideration for anti-oxidation. In order to prevent the dielectric ceramic element assembly from being reduced in the reductive atmosphere, there have been proposals of improving the method of baking, adding a certain specific addition agent to a composition of the dielectric ceramic element assembly. Among the proposals, the Japanese Laid-open Patent No. H6-70944 teaches the following ceramic capacitor:
A ceramic capacitor of low loss rate; comprising
a ceramic dielectric element assembly made of 100 part of
SrTiO3 for 30.0-70.0 weight %,
PbTiO3 for 0.0-40.0 weight %,
Bi2O3 for 8.0-40.0 weight %,
TiO2 for 3.0-20.0 weight %, and
MgO for 1.0-10.0 weight %, plus an addition of
CuO for 0.05-0.7 weight %, CoO for 0.05-3.00 weight % and CeO2 for 0.05-3.00 weight %; and
an electrode made mainly of Cu baked on the opposing surfaces of the ceramic dielectric element assembly.
A Cu electrode or the like base metal electrode for ceramic capacitors, however, need to be baked in a neutral or a reductive atmosphere in view of anti-oxidation. This means that conditions for the neutral or the reductive atmosphere needs to be controlled strictly, which would lead to a deteriorated productivity. Furthermore, should an oxidized base metal electrode actually occur, it not only affects the production yield rate but it significantly impairs the productivity over the total manufacturing process, since it is difficult to detect and select this kind of defects through of a non-destructive inspection process. The adding of a certain specific substance to composition of the dielectric ceramic element represents that the composition ratio needs to be placed under a stringent control, which is another factor of an increased cost.
In order to improve the above-described drawbacks, the Japanese Laid-open Patent No. S63-236785, for example, discloses a process in which a zinc (Zn) paste is applied for baking in the atmospheric air. The U.S. Pat. No. 6,043,973 teaches a ceramic capacitor in which a three-layered electrode is provided by a dry plating method, the first layer of which being Zn. These conventional ceramic capacitors, however, are not provided with any improvement measure that is inexpensive yet effective for suppressing a self heat-generation.
A ceramic capacitor of the present invention comprises a dielectric ceramic element made of any one of the followings as the main constituent:
(A) CaTiO3xe2x80x94La2O3xe2x80x94TiO2,
(B) CaTiO3xe2x80x94La2O3xe2x80x94TiO2xe2x80x94SrTiO3,
(C) SrTiO3xe2x80x94CaTiO3,
(D) SrTiO3xe2x80x94CaTiO3xe2x80x94Bi2O3xe2x80x94TiO2,
(E) SrTiO3xe2x80x94PbTiO3xe2x80x94Bi2/3TiO3 and
(F) SrTiO3xe2x80x94PbTiO3xe2x80x94Bi2/3TiO3xe2x80x94CaTiO3; and
an electrode made mainly of Zn provided on both of the opposing surfaces of the dielectric ceramic element assembly.